TUNNELS TUBOUGU HARD HOCK 105 



withdrawing the tool 2J tons is available. In the rock found at 

 Iselle, namely, antigorio gneiss, a hole j; ins. in diameter and 

 3 ft. 3 ins. in length i> drilled, normally, in 1 '2 mins. to 25 mins. ; 

 a daily rate of advance of 18 ft to 19 ft G ins. is made in a 

 heading having a minimum eross-section of 59 sq. ft. ; the time 

 taken to drill ten to twelve holes, 4 ft. 7 ins. deep, is - ' hrs. 



When the debris resulting from one operation has been 

 sufficiently cleared away, a steel flooring, which is provided 

 near the face to enable shoveling to be more easily done, and 

 to give an even floor for the wheels of the drilling-carriage, is 

 laid bare at the head of the line of mils, and the drilling- 

 machines are brought up on their carriage by eight or ten 

 men. When advanced sufficiently close to the face, the rack- 

 bar is slewed round across the gallery and is wedged up against 

 th'j rock sides ; connection is made between the distributor and 

 the hydraulic main, by means of the flexible pipe, and pressure 

 is supplied by a small copper tube to the rack-bar ram, thereby 

 rigidly holding the machine. Next, connections are made 

 between the three drilling-machines and the di.stributor, and in 

 20 mins. from the time the machine w;is brought up all three 

 drills are hard at work, water pouring from the holes. 



The noise of the motors and grinding-tools is sufficient to 

 drown all but shouts; and where the extension rods do not lit 

 tightly, small jets of water play in all directions, necessitating 

 the wearing of tarpaulins by the men directing the tools. 

 Lighting is done wholly by small oil-lam{is, provided with a 

 hook to facilitate fixing in any crack in the rock; electricity 

 will probably be used to light that portion of the tunnel which 

 is completed. 



Two men are allotted to each drill, one to drive the motor, 

 tin* other to direct and replenish the tool, one foreman and two 

 men in reserve completing the gang. A small hammer is frelv 

 used to loosen the screw joints of the extension rods and drill. 

 A hole is usually commenced by a two-edged flat-pointed tool. 

 until a sufficient depth is reached to prevent the circular tool 



